Effect of Surfactant Monolayer on Reduction of Fe₃O₄ Nanoparticles under Vacuum

Abstract

We study the effects of surfactant monolayer coating on the reduction of Fe 3 O 4 nanoparticles under vacuum thermal annealing. Oleic acid coated and uncoated Fe 3 O 4 nanoparticles were synthesized by a simple coprecipitation technique. In the temperature range of 300-700 °C, the particle size and lattice constant of uncoated Fe 3 O 4 nanoparticles increased from 9 to 18 nm and from 8.357 to 8.446 Å, respectively. On further heating (above 700 °C), Fe 3 O 4 decomposed into γ-Fe 2 O 3 and FeO phases. In the range of 800-1000 °C, the FeO phase was predominant, and its size grew significantly from 30 to 44 nm. Conversion of oleic acid coated Fe 3 O 4 phase to metallic R-Fe commenced at 500 °C and continued up to 800 °C. After vacuum annealing at 800 °C, the magnetic behavior of the sample changed from ferrimagnetic to ferromagnetic. The activation energies for the phase transitions of uncoated and oleic acid coated nanoparticles were estimated to be 30.304 and 17.349 kJ/mol, respectively. Thermogravimetric analysis (TGA) coupled with mass spectrometry revealed that, for coated nanoparticles, effluents such as H 2 , CO, and CO 2 from oleic acid facilitate the reduction of Fe 3 O 4 into R-Fe and FeO during vacuum thermal annealing. The interaction between the headgroup of the oleic acid and the oxygen in Fe 3 O 4 is expected to lead to weakened bonding, which could result in a lower activation energy for the reduction of the surfactant-coated nanoparticles. This is a plausible reason for the precipitatation of R-Fe at lower temperature (at 500 °C) in the surfactant-coated system.

Superior thermal stability of polymer capped Fe3O4 magnetic nanoclusters

“…Figure B shows the variation in crystallite size (ln( d )) against inverse temperature (1/ T ) of PCIO nanoclusters. The estimated value of the activation energy ( E A ) for size growth of PCIO nanoclusters during the temperature range 500°C‐1000°C was 11.781 kJ/mol which is lower than the previous reports on oleic acid coated (17.349 kJ/mol) and uncoated Fe 3 O 4 nanoparticles (30.304 kJ/mol) cases under in‐situ vacuum annealing . The observed difference suggest that the particle growth rate is less in this study.…”

“…On the other hand, Gnanaprakash et al showed that the γ‐Fe 2 O 3 to α‐Fe 2 O 3 phase transition temperature can be enhanced by 150°C (i.e., from 600°C to 750°C) in the presence of trapped Na ions . Interestingly, hydrogen and carbon can also assists the reduction in iron oxide nanoparticles . Chen et al showed that γ‐Fe 2 O 3 nanoparticles located inside the bores of carbon nanotubes are reduced at 600°C, whereas the reduction in γ‐Fe 2 O 3 nanoparticles located on the outer surface of carbon nanotubes happens only at 800°C because of the unique electronic properties of carbon nanotube .…”

Effect of grain size on the magnetic properties of superparamagnetic Ni0.5Zn0.5Fe2O4 nanoparticles by co-precipitation process

“…Furthermore, peaks of some samples, in particular for 650 and 900 1C, shift towards down angles. Ayyappan [23] believe that the growth of nanoparticles can be attributed to coalescence of the particles by solid-state diffusion, where the system reduces its free energy by reducing the surface area of the nanoparticles. On the other hand, changes of diffraction peak sites may be related to lattice expansion, which is consistent with the vibration of lattice constant data in Fig.…”

Effect of Surface Functionalization on the Adsorption of Arsenic Using Magnetite Nanocrystals

“…moisture). The bare-magnetite sample exhibited a second weight loss in the 100-900 °C range that can be attributed to CO 2 release from the decomposition of the adsorbed functional groups of carboxylic acid (Ayyappan et al 2008). In the case of the SO-magnetite sample, the second weight loss step accounted for 5.12% and can be due to the desorption of adsorbed oleate from the nanoparticle surface.…”